Production of photographic silver halide emulsions from gelatinanion soap complexes



Patented Oct. 24, 1956 PRODUCTION or PHOTOGRAPHIC SILVER HALIDEEMULSIONS "FROM GELATIN- ANIoN soar ooMPrExEs v John Alfred Henry Hart,Kenneth George Alfred Pankhurst, and Robert Charles Morris Smith, IlfordEngland, assignors to .Ilford Limited, Ilford, England, a company ofGreat Britain No Drawingr Application October 19, 1945, Se-

rrial No. 623,445. In Great Britain October 30,

This invention relates tothe production of silver halide photographicemulsions.

Whenan anion soap is added to an emulsion of silver halide in gelatin,at alow pI-I- value or in the presence ofan electrolyte (whenthepH valueneed not necessarily be low); a-,.complex is v formed between thegelatin and anion soap and this separates out. carrying the silver"halide with it. 1*. f. It has now been discovered that the gelatin/anionsoapcompl'exesithus formed, and also analogous. complexesformedwith a sulphonic acid containing a highly hydrophobic radicle:in=the anion, are readily dispersible in organic solvents, e. g. methylalcohol. i According to this inven tion', therefore;photographicemulsions i-n -which the solvent mediurnis predominantly organic areformed by dispersing in an organic solvent medium a complex formedbyprecipitating gelatin from its aqueous dispersion containing fsilverhalide in sus'pension, by means of an a'nion'soap, or by means of asulphonic acid "containing a highly hydrophobic radicle in theanion,"the said aqueous dispersion being at a pH value below theisoelectric point of the gelatin, orat a higher pH value and containingan electrolyte. The precipitated complexmay contain a small proportionof water and this be included in the organic solvent dispersion.

According to a further, feature of the invention, there is included in aphotographicemul sion so formed a proportion ofanother colloid which issoluble. in the'solvent medium already present in the emulsion, or whichissoluble in a solvent medium which is miscible with the" solvent mediumalready presentin the emulsion, tov forma stable combination" r Thegelatin/ anion soap complex and analogous complexes formed fromsulphonic;v acids as -defined above, containing silver halide, maybepre"pared by the addition of the anion soap solution to the gelatin silverhalide emulsion and allowing the; gelatin, .complex-to sediment,- out,The complexes maybe redispersedin theorganic solvent medium withoutwashing, but :it is preferred: towash the complex to remove unwanted1ons. responding, free acid: may be employed. 'EIJhe technique ofmaintaining the originalaqueous.

dispersion of the colloid at a low. .pH .value ap- Instead of theanionysoap itself,; the cor-.

17 Claims. (o 95-4) pears to be equivalent in efiect to the use of thefree acid, but the use of the free acid presents the advantage thaltitheresulting complex is not contaminated with the cation of the anion soap.Complexes free from. water-soluble salts are found to be more readilydispersible in some organic solvent media. v

,';-The invention will be described with particular reference to theuseof anion soaps, but it is tobe understood that sulphonic acids which,though not true anion soaps, contain a highly hydro phobic anion, can beused'analogously.

It has been discoveredthat for each particular anion soap there is anoptimum ratio of the soap to-the gelatin which results'inagelatin com.-plex'of; the highest solubility in organic solvents,

and a methodis .availablefor determining such optimum ratio in eachparticular case.

-. If an anion soap is added in gradually in creasing quantity to agelatin solution at: low

" pH, or at higher pH in the presence of electrolyte,

a gelatin/anion soap complex forms and separates out. By measuring theamounts of the anion of the anion soap remaining in the supernatantliquid afterthe mixture has been allowed to stand-f0r some hours, thusreaching equilibrium, and plotting these quantities as ordinates againstthe quantities of anionsoap added as abscissae, using; a logarithmicscale, a curve is obtained showing a straight line rising portionfollowed by a fall where the complex begins. to

separate. The curve falls to a minimum value and thenrises -.again.- Ithas been discovered that, generally; speaking this minimum value(referred to asthe -infiexion point) represents the particularcomplex'having the greatest hydrophobic character andthe greatestsolubility in organic solvents. The precise position of the infiexionpoint, however, depends on Various: fac tors, including the pI-I and thequantity of electrolyte present, if any. H

A curve of this type can be obtained in respect of any particular anionsoap which it is desired to use, and it may be said that, as'a generalproposition, where plain gelatin'is concerned; the

preferred conditions for obtaining the highest degree. of solubilityinorganic solvents are that the anion "of theanion soapusedshould be as:

strongly hydrophobic as possible; the pH of the I. solution should bebelow the isoelectric point of emulsion, it is not always possible toachieve 1 these conditions owing to other factors involved in thetechnique of producingsatisfactory emulsions. For example, it isgenerally'not desirable;

to prepare photographic emulsions at a pH value lower than 3. Moreover,itf-gi's seldom practical to allow the emulsion to stand-with the anionsoap over the long period whichflmay be necessary to obtain equilibriumfAccordingly, the preferred procedure is to ascertain theftrue infiexionpoint using a plain gelatin solution andan anion soap under conditionswhich approximate as closely as possible to the conditions which will benecessitated for a particular gelatin photographic emulsion, and then touse a quantity of anion soap with such emulsion which corresponds tothat'portion of the curve which follows the inflexion point, i. e. touse a concentration of anion soap which is that at the inflexion pointor slightly greater.

Moreover for emulsion-making it is generally desirable that theprecipitated gelatin/anion soap complex should be soluble inwater-miscible solvents since the precipitated complex invariablycontains water, and it is difficult to remove this water withoutadversely afiecting the quality of the emulsion. To this end it isgenerally desirable to treat the-emulsion at a pH below the isoelectricpoint of the gelatin and in the presence of as little electrolyte aspossible, since these conditions appear to favour the production ofcomplexes soluble in water-miscible solvents. To ensure a low pH valueit is preferred to use an emulsion which is at a pH value below theisoelectric point of the gelatin and then to add, either the free acidof the anion soap or the anion soap itself together with sufficientmineral acid to neutralise the cation of the anion soap. J r

Anion soaps are surface-active compounds in which the reduction insurface tension resultant on their addition to wateris due to the anion.The classification of soaps is discussed in the book KolloidchemischeGrundlagen der Textilveredlung by Dr. E. Valko 1937, at pages 519-522,to which reference is made for the meaning of the expression anionsoaps."

Specific classes of compounds fallingwithin this generic expression areas follows:

(a) Soluble salts of long-chain-alkyl carboxylic acids, e. g. solublesalts 'of fatty acids containing 8 or more carbon atoms, as for example,oleic, ricinoleic, linoleic, stearic and palmitic acids. a 1

These, however, are in general much less satisfactory for use than: r

(b) Soluble salts of long-chain-alkyl sulphonic acids. 7

(c) Soluble salts of sulphated higher fatty alcohols, e. g. solublesaltsof fatty alcohol sulphates of which the alkyl group contains at least8-carbon atoms, as for-example the soluble salts of lauryl hydrogensulphate and ole'yl hydrogen sulphate. H I i (d) Soluble salts ofsulphatedsecondary alcohols containing at least 8 carbon atoms in thechain. I

(e) Soluble salts of alkylated aromatic sulphonic acids, e. g. solublesalts of alkyl benzene sulphonic acids, of alkyl naphthalene sulphonicacids and of alkylated hydroxy diphenyl sulphonic acids.

1(f) Soluble salts of long 'ch'ainealkyl esters of sulphated succinicacid; a: 1 I

Thus, it Will be seen that anion soaps containing sulphonic or sulphuricacid groups are preferred to those containing carboxylic acid groups.

The soluble salts may be formed from alkali metals," e. g. sodium andpotassium, from ammonia or from amines, e. g. triethanolamine andcyclohe'xylamine. The anion soaps may contain amino residues in theanion of the soap as, for example, in the sodium salt of oleoyl aminoethane sulphonic acid which contains a carbonamido (NH.CO-) group.

The expression long-chain-alkyl is intended to mean at least 8, andpreferably at least 12,

,. carbon atoms in the alkyl group.

Very many anion soaps are commercially products may conveniently beemployed in the process of this invention. Thus suitable commercialproducts are the compounds sold under the trade names:

Nekal B-X Agral N Aresklene 375 Perminal N Dispersol Santomerse DGardinol Sulphonated Lorol T. A. Igepon T Sulphonated Lorol N. 1-1..Lissapol A Sulphonated Lorol C. Y. Lissapol C Sulphonated OcenolLissatan A- Teepol X Lohrinol Tergitol 4' Nekal A Tergitol 7 I Agral Nis the sodium salt of an alkyl naphthalenesulphonic acid.

Aresklene 375 is the sodium. salt or an alkyloxydiphenyl disulphonicacid.

Dispersol is the sodium salt of dinaphthyl methane disulphonic acid.

Gardinol is an alkali metal sodium long-chainalkyl sulphate of 10 to 18carbon atoms.

Igepon T is the sodium salt-of oleoylmethy1-.

amino-ethane sulphonic acid.

Lissapol A is sodium hexadecyl sulphate. Lissapol C is sodium hexadecylsulphate.

Lissatan A is a condensation product of sodium Sulphonated Ocenol is aSulphonated mixture of aliphatic unsaturated alcohols of 16 to 18 carbonatoms predominating in the latter.

H Teepol X is a mixture of sodium alkyl sulphates of 10 to 18 carbonatoms.

Tergitol 4 and Tergitol 7 are sodium secondaryalkyl sulphates. Suchcommercial detergents and still more the is triethanolarninecyclohexylamine pure. (anion. soaps contained .-in.. them,- are much.preferred to the ordinary ,alkali-metal soaps of, fatty; acids referredto-; -under (a), above.-,. As already indicated, there may be used,insteadof;

theianion soap itself, the free acidderived from such soap.-

As indicated above, instead of true anion soapsh certain sulphonic acidsof which the anion-is,

highlyhydrophobic may be employed. These...

may be simple acids,:for example'2-naphthol-1' sulphonic acid,l-naphtholl-sulphonic acidor anthraquinone-Z-sulphonic acid, or maybemore complex, for example dyestuffs such; as Kiton 3 Fast Yellow 3G(Colour Index No.645) ,which;

contains a sulpho-aryl-pyrazolone radicle} and Naphthalene Orange GS(ImperiaLChemieal- Industries Ltd.)

solvents-for dispersing the complexes are ,-thos e:- i

containing hydroxy groups, erg. methyl and etlh 1,

alcohols,- ethylene glycol mono methyl; eth ethyl lactate and diacetonealcoholt Organ solvents not containing hydroxy groups; are gen erally.only" useful together with some water, orf somehydroxy solvent, e. g;acetone, methyl ethyl kefipne, dioxane, methylene chloride,.,chloro formand' mesityl ,oxide aregpreferablyused in admixture'with water ormethylalcohol. smallquanev titles of esters, e. g. methyl acetate,butyl.aeetate,-,

ethers,.e. gediethyl ether, andhydrocarbons, erg.

benzene and toluene, mayialso, be gincluded inthe,

solvent medium. The choiceof solvent Will' depend onthe particularnature-of;therfcomplex 1 Complexes formed at lowpH and containing arelatively low proportion ofthev anion. soap.,(or; corresponding acid)aregenerally more easily; soluble in polar solvents or; in solventscontaining. some water, whilst those formed at higher,

pH values and containing, more anion soap. (on

corresponding acid) are generally soluble in-non-, polar solvents, e. g.toluene; The complexesmay beswollen in the organic solvent me dirnnzu'id dispersion is usually facilitated by. gentle;.

warming.

As already indicated',=, an important feature of this. invention is theformation of photographic.

emulsions which comprise a gelatin/anion soap complex, containing silverhalide, dispersed in an organic solvent medium, together with a pro:portion of another colloid soluble in such organic solvent medium or inanorganic solvent medium miscible therewith. Suchother colloids may be,for example, cellulose esters, e. g. cellulos nitrate, celluloseacetate, far-hydrolysedcellulose esters (e. g. cellulose acetate havingany acetyl content. of 20 to 30 polyvinyl acetates, poly-,

vinyl acetals, methyl methacrylate polymers and thepartial hydrolysisproducts thereof, .alkyd resins, and mixed interpolymers such as theinterpolymers of maleic acid or anhydride: with styrene or methylmethacrylate. The following examples illustrate the inventlon, but arenot to be regarded as limiting it in any way: 7 V

" Example I 500 cos. of a normal aqueous gelatino silver iodobromideemulsion containing 10% gelatin weremelted and diluted to 4 /2 litreswith water. 'I'o this was added 100 grams of the commercial anion soapAgral N (essentially an alkyl naphthalene sodium sulphonate) dissolvedin 1 litre of: water, and this was followed by 40 cos. of 2N.-

plex (containing suspended silver halide)" 'sep r t d. a .a. mas lr emblnat m It o washed with water, dissolved in 400' cc. warni methyl.valcohol and-reprecipitated by adding, 100

cc. of. water; Adhering liquid was then removed, from the complex byallowing it ,to' drain, and the complex was then. re-dissolved in 400,c'ci warm methyl alcohol to form a satisfactory photographic emulsion.Its sensitometric characteristics ,were. substantially the sam as ,thoseof the original aqueousgelatin emulsion which it was, obtained.

, Example II To a photographic emulsion in methyl alcohol;

obtained in Example I was added, in turn:

Ethylene glycol mono-methylether 400 Low viscosity cellulose nitrater1992, solution in methwl alcohol) 300 Acetone Z 400 The final emulsionso obtained was stable and suitable for coating by the usual techniques.It

ing layer since it adhered strongly tothe lacquer "wasespeciallysuitable, however, for coating by coating both in the drycondition and during all The emulsion developedstages of processing.normally, and it wasfolll d that th coating was not melted by hot water.I

,'In each of thefollowing Examples III to VI the range of'quant'ities ofanion soap employedlieii. on theportion of the curve, referred to above,

which follows the infiexion point asdetermin d undercomparable'conditions in the a bsenc' o "the's'ilver halide and allowingthecomplex separate until equilibrium conditions are reached? ExampleIII Aiwatler-washed gelatin silver halide photo- I graphic emulsion ofhighcontrast characteristics w s d st and s ab l s It s h nd l teq. toa-gelatin concentration of 0.67%, it then con taining 0.51%suspendedsilver halide. The pH of the emulsion was then adjusted to 3.0 by theaddition. of acid.

Portions of the emulsion were then adjusted to a temperature of 509. C.and quantities ofi.

various anion soapsat pI-I 2.2 were added. The

optimum quantities were found to be as follows:

irr 1 a e Der Anion Soap litre of emulsion I V Grams Dodeeyl sodiumsu1phate 2 to 4' Gardinol 3 0; 4 to 15 Agral N 5 to 10 PerminalN q 3.5tolo Aresklene 375 3.5 to 8 1 TeepolX 10 to 30 Sant' mersel') 2.5 to 5;Aresket 240 7.1 to 31.6,. f Igepon 'I 7 to 15 In each case a precipitateof thesilver; ha li'tde;

suspended in a gelatin/anion soap complex,w

formed. Ten minutes after the addition r the anion soap the supernatantliquid was removed by decantation. The complex was then washed'With'water, dispersed in methyl alcohol (109cc.

forothe complex from 1 litre of t e emulsion),

re precipitated with water and re-dlspersed in methyl alcohol. Theresulting dispersion was coated on glass or other convenient support andrlried. v

The resulting emulsion coatings were of satisfactory photographicquality and could be pros-*- essed in a developer of the normalconstitution, fixed and washed in the usual way.

Example IV was of low gelatin concentration, it is not neces sary towork at such low gelatin concentrations; This example illustrates thepreferred conditions for a simple anion soap, Aresket 240, with variousdilutions of the emulsion, the general conditions being as in ExampleIII.

Emulsion Concentration of Aresket 240 Gelatin Con- Silver Conper litreof centration centration emulsion Per Cent Per Cent Grams l. 34 l. 02ll. 3 2.68 2. 04 17.7 4.02 3. 06 25. 2 5. 36 4. 08 29.0 6. 70 5.10 37. 8

The complexes thus obtained are readily'dispersible in methyl. alcoholto form emulsions for coating as in Example II.

EacampZe'V This example illustrates the effect of added electrolyte. 7An emulsion was prepared as in Example III, except that thefpI-I wasadjusted to.7.3 and ammonium nitrate was added to the extent necessaryto form,a 0.5 Normal'solution.

The optimum quantities of anion soap were, found to. be: 1

. Quantityadded Am'on Soap per litre of emulsion Grams Teepol X 30 to 50SantomerseD to v The resulting complexes, containing a substantialamount of adsorbed or absorbed water, were readily dispersible in-methylalcohol to form emulsions suitable for coating as in Example III.

Example VI JIhisexample illustrates the use of a gelatin photographicemulsion of which the gelatin has a high isoelectric point. i

500 cc. of an emulsion made with an acidprocessed gelatin was diluted toa gelatin concentration of 0.67% when it contained 0.5% of suspendedsilver halide. Its pH was-adjusted to 6.0 and 4 cc. of a 63% solution ofAresket 240 was :added, the pH being maintained at 6.0 by furtherhydrochloric acid addition.

Thefre quired complex precipitated and was washed and.-

dispersed in methyl alcohol as in Example; III It will be noted thatthis complex was formed at the relatively high pH 6.0, but in theabsence of added electrolyte.

cipitation under these conditions.

This is only practicable for the reasonthat th gelatin used had anISO-1. electric point about pH 7.5. An emulsion made with normallime-processed gelatin gave no pre- Although in the above examples theprecipitated complexes have been re-dispersedin methyl alcoholtoformemulsions for coating, other water-miscible solvents may be used, forexample ethyl alcohol and ethylene glycol monomethyl ether.

The silver halide emulsions of this inventory 1 may contain any of theusual additions to silver halide emulsions, e. g. optical sensitisingdyes,

sulphur sensitisers as for instance allyl isothiocyanate, gold salts asdescribed in British Patent) No. 570,393 and corresponding United StatesPatent -N0. 2,399,083, stabilisers, anti-fogging agents, toning agentsand other agents for modifying the speed, contrast, graininess, fogleveland image colour of the products.

The invention provides photographic emulsions having a gelatin basisdispersed in organic solvent and the emulsions are therefore of value ina" number of special applications. As already indicated they are ofparticular value for spray coating. Normal gelatin silver halideemulsions present considerable difliculties in spray coating since it isusually necessary to maintain the emulsion warm in the spray-gun toprevent it setting therein. Moreover, the ordinary emulvisionswill notadhere firmly if sprayed on to lacquered metal sheet. Emulsions may beprepared according to this invention, however, which have littletendency to set in the spray-gun. Moreover, the organic solvent usuallyhas a slight solvent action on lacquered surfaces and thus facilitatesadhesion between such surfaces and the emulsion sprayed thereon.

The spray-coating of lacquered metal sheets with photographic emulsionis of particular value in the production of photo-templates. -In thecommercial application of this process, however,- the users generallyprefer that the emulsion should be supplied in dry granular conditionsothat it may be re-dispersed when required to form an emulsion suitablefor spraying. present emulsions are especially suitabl in thisconnection. Emulsions prepared in organic solvent media according tothis invention can easily be dried by the well-known expedients of filmdrying, spray drying, and air drying of the emulsion in the form of ashredded set jelly, since the organic solvent readily evaporates. Afurthermethod is to precipitate the emulsion by adding it to water and,after breaking up the precipitate, to air-dry the product. The followingspecific Example VII illustrates this techni'que. In this example theemulsion contains a matting agent, though this is not essential.

Example VII 200 grams of a gelatin silver halide emulsion: were meltedat F. and to this was added 4- grams of Celite 204 (a commercial form ofpurified diatomaceous earth) dispersed in 600 cc; water containing 0.4gm. gelatin. To the prod uct was added 35 cc. of Teepol X and themixture' stirred. 25 cc. of normal hydrochloric acid was then added, themixture allowed to stand for 15 minutes and the supernatant liquiddecanted. The precipitate was washed with 500 cc. water for 2 minutesand the washing liquid decanted. The precipitate was then dissolved in100 cc. of methyl alcohol at F. and then repricipitated by adding 75 cc.of distilled water.

The precipitate was then re-dissolved in 200 cc. methyl alcohol at 125F., and 15 grams of cellu lose nitrate and 200 cc. of acetone wereadded.

200 cc. of the resulting emulsion was poured into 1 litre of colddistilled water and stirred. f

The resulting precipitate was shredded, soaked for 10 minutes in 500 cc.water, and then spread The out to dry. The lumps dried without adheringto one another to any serious extent.

Another useful method of forming dried emul-v sions from the emulsionsin organic solvent prepared according to thisqinvention consists inshredding-the set jelly emulsion into water and then air-drying theshreds. This method is illustrated in" the following Example VIII.

' E ample VIII I An emulsion was prepared as in Example VII It was setto a jelly and shredded by pressing through a perforated plate intowater. About 200 cc. of the emulsion was shredded in this way for 30minutes and then melting at 125 F.

A dried emulsion suitable for re-constituting in water or aqueousalcohol can be made by a similar method, "the cellulose nitrate beingomitted. Re-constitution can be effected bysoaking in water containingsufiicient sodium bicarbonate to neutralise the acid and melting at 120F. An emulsion suitable for spraying can be made; by using 50 grams ofthe dried emulsion-shreds, 2 grams of sodium bicarbonate, 500 cc. ofwater and 500 cc. of ethyl alcohol (64 O.'P.).- "1

The emulsions 'of this invention, either as originally prepared or as re-constituted after drying, can be used in any process wher spraycoatingis required. The production of phototemplates has alreadybeen mentioned,and another useful application is in the preparation of dials,nameplates and the like on metal or other surfaces. A furtherapplication is in the preparation of silk-screen printing surfaces. Inthis application the emulsion is sprayed on to stretched silk, dried,exposed, developed in a tanning developer and washed in hot water toproduce a wash-out relief image. It is a peculiar characteristic of theemulsions of this invention that, though quite insoluble in water whencoated, they tend to become soluble when allowed to stand in contactwith alkali, as in normal development, though the emulsions are stillnot soluble in water except at high temperatures. Fixing in an acidfixing bath however; restores the ins'olubility of the complex even inhot water. Thus a suitable technique for using the emulsions in theproduction of silk screen relief images is to develop the exposed imagein alkaline pyrocatechol, plunge the silk into hot water and then to-fixthe wash-out relief image. An alternative technique is to prepare thewash-out relief image on a support from which it may be stripped and totransfer the image to a silk support.

The emulsions .of this. invention are also of value in colourphotography. Thus they may contain dyes or. dye-intermediates, e. g.colourformers which react with the oxidation products of aromaticprimary amino developing agents-to form quinone-imine .or azoemethinedyes, the colour-former being uniformly dispersed in the emulsion. Thecolour-former, especially where particulate or of very highumolecularweight,

.1 may be included in the original emulsion and precipitated with thecomplex, or it may be added tothe final emulsion. Many of thhighmolecular weight colour-formers, which are preferred from thestandpoint of being non-difiusing in the emulsion, are difficult todisperse in ordinary aqueous gelatin silver halid 'e'mulsions, but muchmore easily dispersed in the organic solvent emulsions ofthis invention.

The emulsions of this invention are permeable to ordinary alkalinedevelopers, but the degree of permeability depends on the preciseconstitution of the emulsion. By a suitable selection. of an additionalcolloid, e. g. cellulose nitrate ora hydrophobic acid colloid,emulsions'of varying degree of developer-permeability may be made; andaccordingly it is possible to build up a multilayer photographicmaterial for'colour photography in which the several layers havedifferent degrees of permeability to ordinary developers and,- byadjusting the constitution of the developers, e. g. by adding organicsolvents, to develop each of the layersseparately. In such a process, byusing aromatic primary amino developing agents containing differentcolourformers, images indifferent colours may be formed in the variouslayers, and by a suitable selection of colour-formers a finaltrue-colour image may be obtained.

Another use to which the emulsions of this invention may be put isin theproduction of printing paper to be used for printing from Wet negatives.As already stated the emulsions of this invention have a good resistanceto water, though they are readily developed by ordinary alkalinedeveloping'solutions. Paper coated with emulsion according to thisinvention may be used for printing from wet negatives, though it isusually desirable to employ an emulsion containing a proportion of othercolloids, e. g; cellulose nitrate and a methyl methacrylate-methacrylicacid co-polymer. Such emulsions not only have a good resistance to waterbut also a good resistance to hypo, which may be carried by the wetnegative. Advantageously, in the production of weteprinting paper usingthe emulsions of this invention the emulsion should be supercoated witha layer of a plain gelatin/anion soap complex in organic solvent, asdescribed in our copending United States application Serial No. 623,446,filed October 19, 1945, now Patent No'. 2,527,262, corresponding toBritish applications NOS. 21,092/44 and 24,779/44.

What we claim is: I I I r ,I

1. 'Aphotographic emulsion comprising a dis persionin a predominantlyorganic solvent me,- dium of a complex of gelatin with an anion soapwhich is soluble in a solution composed of methyl alcohol, said complexbeing the essential binding agent for light-sensitive silver halidegrains which are dispersedtherethrough.

e 2. A photographic emulsion comprising a dis persion in a predominantlyorganic solvent medium of a complex of gelatin with an anion soapcontaining a sulphur acid group which is soluble in a solution composedof methyl alcohol, said complex being the essential binding agent forlight-sensitive silver 'halide grains which are dispersed therethrough;

3. A photographic emulsion comprising a dispersion in 'a predominantlyorganic solvent medium of a; complex of gelatin with a water-solublesalt of a sulphate'd higher fatty alcohol which is solublein a solutioncomposed of methyl alcohol, said complex-being the essential bindingagent for light-sensitive silver halide grains which are dispersedtherethrough.

4. A photograhpic emulsion comprising a dispersion in a predominantlyorganic solvent me-' dium of a complex of gelatin with an anion soapwhich is soluble in a solution composed of methyl alcohol, said complexbeing the essential binding agent for light-sensitive silver halidegrains which are dispersed therethrough, said emulsion furthercontaining a proportion of another colloid which is soluble in the saidsolvent medium.

5. A photographic emulsion comprising a dispersion in a predominantlyorganic solvent medium of a complex of gelatin with a water-soluble saltof a long-chain-alkyl sulphonic acid which is soluble in a solutioncomposed of methyl alcohol, said complex being the essential bindingagent for light-sensitive silver halide grains which are dispersedtherethrough, said emulsion further containing a proportion of anothercolloid which is soluble in the said solvent medium.

6. A photographic emulsion comprising a dispersion in a predominantlyorganic solvent medium of a complex of gelatin with a water-soluble saltof a sulphated higher fatty alcohol which is soluble in a, solutioncomposed of methyl alcohol, said complex being the essential bindingagent for light-sensitive silver halide grains which are dispersedtherethrough, said emulsion further containing a proportion of cellulosenitrate.

7. A photographic emulsion comprising a dispersion in a predominantlyorganic solvent medium of a complex of gelatin with a water-soluble saltof a long-chain-alkyl sulphonic acid which is solubly in a solutioncomposed of methyl alcohol, said complex being the essential bindingagent for light-sensitive silver halide rains which are dispersedtherethrough, said emulsion further containing a pro-portion ofcellulose nitrate and a proportion of a hydrophobic acid colloid.

8. A photographic emulsion comprising a dispersion in a predominantlyorganic solvent medium containing methyl alcohol of a complex of gelatinwith an anion soap which is soluble in a solution composed of methylalcohol, said complex being the essential binding agent forlight-sensitive silver halide grains which are dispersed therethrough.

9. A photographic emulsion comprising a dispersion in a predominantlyorganic solvent medium containing methyl alcohol of a complex of gelatinwith a Water-soluble salt of a sulphated higher fatty alcohol which issoluble in a solution composed of methyl alcohol, said complex being theessential binding agent for light-sensitive silver halide grains whichare dispersed therethrough.

10. A photographic emulsion comprising a dispersion in a predominantlyorganic solvent medium containing methyl alcohol and acetone of acomplex of gelatin with an anion soap which is soluble in a solutioncomposed of methyl alcohol, said complex being the essential bindingagent for light-sensitive silver halide grains which are dispersedtherethrough, said emulsion further containing a proportion of anothercolloid which is soluble in the said solvent medium.

11. A method for the production of photographic emulsion in apredominantly organic sol- =2 vent medium which comprises forming anemulsion of silver halide in an aqueous solution of gelatin, adding tosuch emulsion an anion soap in a concentration near the inflexion pointat a pH below the isoelectric point of the gelatin and in the'presenceof a minimum concentration of electrolyte whereby a complex of gelatinand the anion soap is precipitated which is soluble in a solutioncomposed of methyl alcohol and contains the dispersed silver halide andredispersing the said complex with the dispersed silver halide in apredominantly organic solvent medium. l

12. A method for the production of photographic emulsion in apredominantly organic solvent containing hydroxyl groups which comprisesforming an emulsion of silver halide in an aqueous solution of gelatin,adding to such emulsion an anion soap in a concentration near theinflexion point at a pH below the isoelectric point of the gelatin andin the presence of a minimum concentration of electrolyte whereby acomplex of gelatin and the anion soap is precipitated which is solublein a solution composed of methyl alcohol and contains the dispersedsilver halide and redispersing the said complex with the dispersedsilver halide in a predominantly organic solvent containing hydroxylgroups.

13. A method for the production of photographic emulsion in apredominantly organic solvent medium which comprises forming an emulsionof silver halide in an aqueous solution of gelatin, adding to suchemulsion an anion soap containing a sulphur acid grouping in aconcentration near the infiexion point at a pH below the isoelectricpoint of the gelatin and in'the presence of a minimum concentration ofelectrolyte whereby a complex of gelatin and the anion soap isprecipitated which is soluble in a solution composed of methylalcohol-and contains the dis persed silver halide and redispersing thesaid complex with the dispersed silver halide in a, predominantlyorganic solvent medium.

14. A method for the production of photographic emulsion in apredominantly organic solvent medium which comprises forming an emulsionof silver halide in an aqueous solution of gelatin, adding to suchsolution ata pH below the isoelectric point of the gelatin an anion soapcontaining a sulphonic acid grouping, in a concentration near theinflexion point and in the presence of a minimum concentration ofelectrolyte whereby a complex of gelatin and the anion soap isprecipitated which is soluble in a solution composed of methyl alcoholand contains the dispersed silver halide and redispersing said complexwith the dispersed silver halide ina predominantly organic solventmedium.

15. A method for the production of photographic emulsion in apredominantly organic solvent medium which comprises forming an emulsionof silver halide in an aqueous solution of gelatin, a water-soluble.salt of a long chain alk'yl sulphonic acid, in a. concentration nearthe inflexion point at a pH below the isoelectric point of the gelatinand in the presence of a minimum of electrolyte whereby a complex ofgelatin and said salt is precipitated which is soluble in a solutioncomposed of methyl alcohol and contains the dispersed silver halide andredispersing said complex with the dispersed silver halide in apredominantly organic solvent medium.

16. A method for the production of photographic emulsion in apredominantly organic solvent medium which comprises forming an'emulsionof silver halide in an aqueous solution of gelatin, a water-soluble saltof a sulphated higher fatty alcohol, in a concentration near theinfiexion point at a pH below the isoelectric point of the gelatin andin the presence of a minimum of electrolyte whereby a complex ofgelatinan'd 13 said salt is precipitated which is soluble in a'solutioncomposed of methyl alcohol and contains the dispersed silver halide andredispersing said complex with the dispersed silver halide in apredominantly organic solvent medium.

17. A method for the production of photographic emulsion in apredominantly organic solvent medium which comprises forming an emulsionof silver halide in an aqueous solution of gelatin, a water-soluble saltof a long chain alkyl sulphonic acid, in a concentration near theinflexion point at a pH below the isoelectric point of the gelatin andin the presence of a minimum of electrolyte whereby a complex of gelatinand said salt is precipitated which is soluble in a solution composed ofmethyl alcohol and contains the dispersed silver halide and redispersingsaid complex with the dispersed silver halide in a predominantly organicsolvent medium, washing said complex with the dispersed silver halide,drying it down to granular form and redispersing it in a predominantlyorganic solvent medium.

JOHN ALFRED HENRY HART. KENNETH GEORGE ALFRED PANKHURST. ROBERT CHARLESMORRIS SMITH.

14 REFERENCES CITED The following references are of record in the fileof this patent:

UNITED STATES PATENTS Number Name Date 1,290,794 Sheppard Jan. 7, 19191,844,716 Lambert Feb. 9, 1932 2,142,311 Heidenhain Jan. 3, 19392,258,755 Glaser Oct. 14, 1941 2,282,001 Russell et a1. May 5, 19422,304,940 'Mannes et a1. Dec. 15, 1942 2,324,831 Frohlich et al 1. July20, 1943 2,489,341 Waller et al Nov. 29, 1949 FOREIGN PATENTS NumberCountry Date 537,256 Great Britain June 16, 1941 556,360 Great BritainOct. 1, 1943 OTHER REFERENCES Journal of the American Chemical Society,De-

cember 1943, pages 2187-2190 and May 1944, pages

1. A PHOTOGRAPHIC EMULSION COMPRISING A DISPERSION IN A PREDOMINANTLYORGANIC SOLVENT MEDIUM OF A COMPLEX OF GELATIN WITH AN ANION SOAP WHICHIS SOLUBLE IN A SOLUTION COMPOSED OF METHYL ALCOHOL, SAID COMPLEX BEINGTHE ESSENTIAL BINDING AGENT FOR LIGHT-SENSITIVE SILVER HALIDE GRAINSWHICH ARE DISPERSED THERETHROUGH.